1. Field of the Invention
This invention relates generally to a crank shaft support assembly for increasing stiffness and reducing thermal mismatch distortion in a crank shaft bore of an engine comprising different materials.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
It is known for internal combustion engines that have cylinder blocks comprising lightweight metals such as magnesium, to include a crank shaft support assemblies that include heavier, stiffer metals such as cast iron, and that are designed to reduce thermal mismatch distortion in a crank shaft bore of the engine. For example, the internal combustion engine cylinder crankcase disclosed in German patent document DE 10021198 B4, discloses a crank shaft support assembly including a magnesium cylinder block including an insert-molded ferrous skeleton that extends into a series of crank journals of the cylinder block. The skeleton comprises a metal such as cast iron or steel or a metal alloy that has high stiffness and a low thermal coefficient of expansion. A series of bearing clamps are bolted to the crank journals to form spaced-apart crank shaft support rings defining a crank shaft bore. Each bearing clamp comprises magnesium but also includes an insert-molded ferrous bearing clamp insert. The crank shaft support assembly of the German patent includes a pair of parallel magnesium skirt walls that connect outer edges of the bearing clamps and are formed with the bearing clamps as a single unitary ladder structure. The entire skirt and bearing clamp structure is bolted to the ferrous skeleton of the cylinder block by bolts extending through ferrous screw bus portions of the bearing clamp inserts. However, a crank shaft support assembly constructed according to the German patent is limited in its ability to reduce thermal mismatch stresses and distortions because its bearing clamps are supported directly on and are connected to magnesium cylinder block structures. This direct support of the bearing clamps on the magnesium cylinder block can result in a “banana” distortion effect of the crank journals and bearing clamps along the y (crank bore) axis.
What is needed is a crank shaft support assembly that further increases stiffness and reduces thermal mismatch distortion in a crank shaft bore of an engine comprising different metals.